Slide 1
2. ANALOGUE ELECTRONICS.
Slide 2
Magnitude Unit
Voltage (V)
Electric current (I)
Power (P)
Electric resistance (Ω)
Symbol of a resistor
1a. Remember the main electrical magnitudes and find the unit for each one: Watt (W) Volts (V) Ohms (Ω) Ampere (A)
Image of a resistor
2.1. Resistors.
Resistors are components which resist the flow of electricity through a circuit for a given voltage. A resistor implements electrical resistance.
Slide 3
Magnitude Unit
Voltage (V) Volts (V)
Electric current (I) Ampere (A)
Power (P) Watt (W)
Electric resistance (Ω) Ohms (Ω)
Symbol of a resistor
1a. Remember the main electrical magnitudes and find the unit for each one:
Image of a resistor
2.1. Resistors.
Resistors are components which resist the flow of electricity through a circuit for a given voltage. A resistor implements electrical resistance.
Slide 4
OHM’S LAW connects resistance, voltage and current in an electrical circuit.
a) Formula for finding the voltage across a resistor for a given current.
b) Formula for finding the current through a resistor for a given voltage.
[ _ ] The voltage (V) across a resistor is proportional to the current (I) passing through it, where the constant of proportionality is the resistance (R).
[ _ ] When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage.
[ _ ] Voltage across a resistor equals the current through it multiplied by the resistance.
[ _ ] Current through a resistor equals the voltage across it divided by the resistance.
1b. Which formula represents these formulations of Ohm’s law better, a) or b)?
Slide 5
OHM’S LAW connects resistance, voltage and current in an electrical circuit.
a) Formula for finding the voltage across a resistor for a given current.
b) Formula for finding the current through a resistor for a given voltage.
[ a ] The voltage (V) across a resistor is proportional to the current (I) passing through it, where the constant of proportionality is the resistance (R).
[ b ] When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage.
[ a ] Voltage across a resistor equals the current through it multiplied by the resistance.
[ b ] Current through a resistor equals the voltage across it divided by the resistance.
1b. Which formula represents these formulations of Ohm’s law better, a) or b)?
slide Slide 6
1c. Choose the right answer or answers.
a) The higher the resistance, the lower the current.
b) The higher the resistance, the higher the current.
c) The lower the resistance, the higher the current.
d) The lower the resistance, the lower the current.
slide Slide 7
1c. Choose the right answer or answers.
a) The higher the resistance, the lower the current.
b) The higher the resistance, the higher the current.
c) The lower the resistance, the higher the current.
d) The lower the resistance, the lower the current.
slide Slide 8
1d. In this circuit, R can be 0.5 Ω, 1 Ω or 2 Ω. Identify which resistance corresponds to each graph. .
+
_V
I
R
R=
R= 1 Ω
R=
V
I R=
R=
R=
I
V
a) b)
The lowerThe higher
the resistance,the lowerthe higher
the currentthe voltage
for a givenvoltage.current.
Construct a sentence that makes sense for graph a) and one for graph b).
a)
The ...........................................................................................................
......
b)
The ...........................................................................................................
....
slide Slide 9
1d. In this circuit, R can be 0.5 Ω, 1 Ω or 2 Ω. Identify which resistance corresponds to each graph. .
+
_V
I
R
R= 0.5 Ω
R= 1 Ω
R= 2 Ω
V
I R= 2 Ω
R= 1 Ω
R= 0.5 Ω
I
V
a) b)
The lowerThe higher
the resistance,the lowerthe higher
the currentthe voltage
for a givenvoltage.current.
Construct a sentence that makes sense for graph a) and one for graph b).
a) The higher the resistance the lower the current for a given
voltage.
b) The higher the resistance the higher the voltage for a given
current.
slide Slide 10
The Ω is too small for many resistors. Then we use the MULTIPLES kilo (k) and mega (M). Sometimes, to avoid reading errors, the letters
R,k and M substitute the decimal point.
4k7 = 4.7 kΩ = 4,700 Ω 5M6 = 5.6 MΩ = 5,600,000 Ω
3R3 = 3.3 Ω
2a. Give the value in Ω for the following resistors.
Write the answers like the example:
a) 6k8 =b) 1M2 =c) 47R =d) 5R6 =
5M6: five point six mega-ohms are five million six hundred thousand Ω.
a) 6k8:
b) 1M2:
c) 47R:
d) 5R6:
slide Slide 11
The Ω is too small for many resistors. Then we use the MULTIPLES kilo (k) and mega (M). Sometimes, to avoid reading errors, the letters
R,k and M substitute the decimal point.
4k7 = 4.7 kΩ = 4,700 Ω 5M6 = 5.6 MΩ = 5,600,000 Ω
3R3 = 3.3 Ω
2a. Give the value in Ω for the following resistors.
Write the answers like the example:
a) 6k8 = 6,800 Ωb) 1M2 = 1,200,000 Ωc) 47R = 47 Ωd) 5R6 = 5.6 Ω
5M6: five point six mega-ohms are five million six hundred thousand Ω.
a) 6k8: six point eight kilo-ohms are six thousand eight hundred Ω.
b) 1M2: one point two mega-ohms are one million two hundred thousand Ω.
c) 47R: forty-seven Ω.
d) 5R6: five point six Ω.
slide Slide 12
2b. Now apply Ohm’s law to calculate the current through the resistors as in the example. When you finish, check the answers with your partner
without reading their workbook.
+
5V
I?
6M6
Remember: 0.001 A = 1 mA and 0.000001 A = 1µA
+
5V
I?
6M6
a)
What result did you get for part a)?
slide Slide 13
2b. Now apply Ohm’s law to calculate the current through the resistors as in the example. When you finish, check the answers with your partner
without reading their workbook.
+
5V
I?
6M6
Remember: 0.001 A = 1 mA and 0.000001 A = 1µA
+
5V
I?
6M6
a)
What result did you get for part a)?
slide Slide 14
2b.
+
5V
I?
6M6
+
5V
I?
6M6
b)
c)
+
5V
I?
6M6
d)
slide Slide 15
2b.
+
5V
I?
6M6
+
5V
I?
6M6
b)
c)
+
5V
I?
6M6
d)
slide Slide 16
3a. Fill in the blanks looking at the table below.
A lot of resistors have coloured rings on them instead of numbers. Each colour stands for a different unit: black is zero, brown is ___ , red is two; orange is three; yellow is ___; green is five; __ _ is six; violet is seven; grey is ____; white is nine, as you can see in the table below.
The first band is for tens and the second band forunits. The third band is the multiplier.
Ex.: red / violet / green stands for 2 / 7 / 00000, that is 2,700,000 Ω.
1st colour band 2nd colour band Multiplier Tolerance
Black 0 Black 0 Silver divide by 0.01 Silver 10%
Brown 1 Brown 1 Gold divide by 0.1 Gold 5%
Red 2 Red 2 Black multiply by 1 Red 2%
Orange 3 Orange 3 Brown multiply by 10
Yellow 4 Yellow 4 Red multiply by 100
Green 5 Green 5 Orange multiply by 1,000
Blue 6 Blue 6 Yellow multiply by 10,000
Violet 7 Violet 7 Green multiply by 100,000
Grey 8 Grey 8 Blue multiply by 1,000,000
White 9 White 9
slide Slide 17
3a. Fill in the blanks looking at the table below.
A lot of resistors have coloured rings on them instead of numbers. Each colour stands for a different unit: black is zero, brown is one, red is two; orange is three; yellow is four; green is five; blue is six; violet is seven; grey is eight; white is nine, as you can see in the table below.
The first band is for tens and the second band forunits. The third band is the multiplier.
Ex.: red / violet / green stands for 2 / 7 / 00000, that is 2,700,000 Ω.
1st colour band 2nd colour band Multiplier Tolerance
Black 0 Black 0 Silver divide by 0.01 Silver 10%
Brown 1 Brown 1 Gold divide by 0.1 Gold 5%
Red 2 Red 2 Black multiply by 1 Red 2%
Orange 3 Orange 3 Brown multiply by 10
Yellow 4 Yellow 4 Red multiply by 100
Green 5 Green 5 Orange multiply by 1,000
Blue 6 Blue 6 Yellow multiply by 10,000
Violet 7 Violet 7 Green multiply by 100,000
Grey 8 Grey 8 Blue multiply by 1,000,000
White 9 White 9
slide Slide 18
3b. Obtain the value of these resistors:
a) Brown / green / red:
b) Orange / orange / brown:
c) Green / grey / yellow:
d) Yellow /violet / orange:
Express the previous values with M or k if possible.For example, 27000 Ω= 27 kΩ
slide Slide 19
3b. Obtain the value of these resistors:
a) Brown / green / red: 1/5/00= 1,500 Ω = 1.5 kΩ
b) Orange / orange / brown: 3/3/0= 330 Ω
c) Green / grey / yellow: 5/8/0000= 580,000 Ω = 580 kΩ
d) Yellow /violet / orange: 4/7/000= 47,000 Ω = 47 kΩ
Express the previous values with M or k if possible.For example, 27000 Ω= 27 kΩ
slide Slide 20
Manufacturers of the resistors cannot guarantee an exact value.The fourth band expresses the TOLERANCE in %.
Red /violet / orange //silver
R =27000 Ω ±10%
10% of 27000 = 27000·10/100=2700
R = 27000 Ω ± 2700 Ω
Minimum value =27000-270=26730 Ω
Maximum value = 27000+270=27270
slide Slide 21
Colours Value Tol. % Tol. Minimum Maximum
Red /violet / orange //silver 27000 Ω 10% 2700 26,730 Ω 27,270 Ω
Brown / green / red // silver
Orange / orange / brown // gold
Green / grey / yellow // silver
Yellow /violet / orange // gold
3c. Calculate the minimum and maximum real values for these four resistors:
slide Slide 22
Colours Value Tol. % Tol. Minimum Maximum
Red /violet / orange //silver 27000 Ω 10% 2700 26,730 Ω 27,270 Ω
Brown / green / red // silver 1500 Ω 10% 150 1,350 Ω 1,650 Ω
Orange / orange / brown // gold 330 Ω 5% 16.5 313.5 Ω 346.5 Ω
Green / grey / yellow // silver 580000 Ω 10% 58000 522,000 Ω 638,000 Ω
Yellow /violet / orange // gold 47000 Ω 5% 2350 44650 Ω 49,350 Ω
3c. Calculate the minimum and maximum real values for these four resistors:
slide Slide 23
3d. Work with your partner in turns. Choose 1 resistor from the pool and write down its colours. Then you have to tell your partner the
colours and he has to find out the value.
1kΩ
120Ω
1.5 kΩ1.2 kΩ
1.8 MΩ
18 Ω
2200 Ω
820 Ω
270 kΩ
270 Ω
3.3 MΩ
330 kΩ
390 Ω4700 kΩ 47 kΩ5.6 kΩ
680 kΩ
8.2 kΩ
- My resistor is brown, black, red.- Yes, it is. You are right…
- Is it 1000 Ω?- My resistor is …
slide Slide 24
3e. Your teacher will give you one real resistor. Note down the colours, calculate its value and write the text to describe your resistor to the class.3e. Your teacher will give you one real resistor. Note down the colours,
calculate its value and write the text to describe your resistor to the class.
The first band colour of my resistor is......
The quoted value is .......................... The tolerance is...The minimum…
slide Slide 25
Fixed resistors are the most common type of resistor.
Variable resistors are also known as potentiometers. They are used
to act on a circuit, for example to adjust sensitivity or to change gain.
They have 3 legs. The resistance between the two outside legs (RAB)
is fixed. By moving the middle leg or cursor, we adjust the resistance
between the middle leg and the outside legs.
The three values are linked like this: RAB= RAC + RCB.
A
B
C10k5 k
_ k
A
B
C10k2 k
_ k
A
BC
10k8 k
_ k
4a. Can you get the values for RCB in these 10 kΩ potentiometers?
slide Slide 26
Fixed resistors are the most common type of resistor.
Variable resistors are also known as potentiometers. They are used
to act on a circuit, for example to adjust sensitivity or to change gain.
They have 3 legs. The resistance between the two outside legs (RAB)
is fixed. By moving the middle leg or cursor, we adjust the resistance
between the middle leg and the outside legs.
The three values are linked like this: RAB= RAC + RCB.
A
B
C10k5 k
5 k
A
B
C10k2 k
8 k
A
BC
10k8 k
2 k
4a. Can you get the values for RCB in these 10 kΩ potentiometers?
slide Slide 27
Special resistors change resistance as a result of a change in other magnitudes. They are used in sensing circuits.
Name Depending on Coefficient Symbol
NTC Thermistors Temperature Negative
PTC Thermistors Temperature Positive
Light-dependent resistors (LDRs)
Light Negative
_
+
slide Slide 28
4b. Explain how the special resistor works as in the model:
NTC thermistors’ resistance changes according to the temperature. As
temperature goes up, the resistance goes down. They are used in
temperature-sensing circuits.
PTC ....
LDR ....
slide Slide 29
4b. Explain how the special resistor works as in the model:
NTC thermistors’ resistance changes according to the temperature. As
temperature goes up, the resistance goes down. They are used in
temperature-sensing circuits.
PTC thermistors’ resistance changes according to the temperature. As
temperature goes up, the resistance goes up. They are used in
temperature-sensing circuits.
LDR’s resistance changes according to light. As light is brighter, the
resistance goes down. They are used in light-sensing circuits.
slide Slide 30
4c. Complete the visual organizer.
Resistors
- ________ resistors.
- Variable or _______________
- ______________
- _____________
- _____________
- _____________
+
-
slide Slide 31
4c. Complete the visual organizer.
Resistors
- Fixed resistors.
- Variable or potentiometers.
- Special resistors
- NTC thermistors
- PTC thermistors
- LDR’s
+
-
slide Slide 32
POTENTIAL or VOLTAGE DIVIDERS are used for dividing up the
voltage, so that parts of a circuit receive only the voltage they require.
+
VinI
R1
R2 Vout
They usually consist of two resistors connected in series across a
power supply. Potential dividers are used, for example, with LDRs in
circuits which detect changes in light.
slide Slide 33
5a. Calculate Vout by applying the formula of a voltage divider.
+
Vin= 9V
I
R1=20Ω
R2=10Ω
Vout
slide Slide 34
5a. Calculate Vout by applying the formula of a voltage divider.
+
Vin= 9V
I
R1=20Ω
R2=10Ω
Vout
slide Slide 35
5b. When one of the resistors is a special resistor the circuit is a sensor. Predict how light changes will affect Vout.
+Vin R1
R2 Vout
Light goes up
R2 goes ___
Vout goes ___
Light goes down
R2 goes ___
Vout goes ___
cause
effectcause
effect
•What is the effect of light going down? ....
•What is the cause of Vout going up? .....
slide Slide 36
5b. When one of the resistors is a special resistor, the circuit is a sensor. Predict how light changes will affect Vout.
+Vin R1
R2 Vout
Light goes up
R2 goes down
Vout goes down
Light goes down
R2 goes up
Vout goes up
cause
effectcause
effect
•What is the effect of light going down? If light goes down, Vout goes up.
•What is the cause of Vout going up? Vout goes up if light goes down.
slide Slide 37
5c. Calculate the minimum and maximum values of Vout that we can get by adjusting the potentiometer.
+
Vin= 9V 10kΩ
10kΩ
Vout10kΩ
slide Slide 38
Cursor at the top end:
R1=10k and R2=20k
Cursor at the bottom end:
R1=20k and R2=10k
5c. Calculate the minimum and maximum values of Vout that we can get by adjusting the potentiometer.
+
Vin= 9V 10kΩ
10kΩ
Vout10kΩ
slide Slide 39
2.2. Capacitors.
6a. Listen and fill in the gaps in this text about capacitors.
A capacitor is a discrete component which can store an electrical
charge. The larger the __________ the more ________ it can store.
Capacitors are used in _______ circuits, filter _______ and as _______
devices.
Symbol
u2a6.mp3
slide Slide 40
2.2. Capacitors.
6a. Listen and fill the gaps in this text about capacitors.
A capacitor is a discrete component which can store an electrical
charge. The larger the capacitance the more charge it can store.
Capacitors are used in timing circuits, filter signals and as sensing
devices.
Symbol
slide Slide 41
The unit of capacitance is the Farad. As this is a large amount, these submultiples are used.
micro-Farad (µF)1 µF =10-6 F
1 µF = 0.000001 F
nano-Farad (nF)1 nF = 10-9 F
1 nF = 0.000000001 F
pico-Farad (pF)1 pF = 10-12 F
1 pF = 0.000000000001 F
1 F= 1,000,000 µF = 1,000,000,000 nF = 1,000,000,000,000 pF
6b. Convert these values to Farads as in the example. Check answers with your partner.
a) 100 pF =
b) 10 µF =
c) 0.1 µF =
d) 68 nF =
Example: 33 nF = 0.000000033 F = 33·10-9 F
slide Slide 42
The unit of capacitance is the Farad. As this is a large amount, these submultiples are used.
micro-Farad (µF)1 µF =10-6 F
1 µF = 0.000001 F
nano-Farad (nF)1 nF = 10-9 F
1 nF = 0.000000001 F
pico-Farad (pF)1 pF = 10-12 F
1 pF = 0.000000000001 F
1 F= 1,000,000 µF = 1,000,000,000 nF = 1,000,000,000,000 pF
6b. Convert these values to Farads as in the example. Check answers with your partner.
a) 100 pF = 0.0000001 F = 100·10-9 F
b) 10 µF = 0.00001 F = 10·10-6 F
c) 0.1 µF = 0.0000001 F =100·10-9 F
d) 68 nF = 0.000000068 F = 68·10-9 F
Example: 33 nF = 0.000000033 F = 33·10-9 F
slide Slide 43
6c. Read the text and then answer the questions.
The small capacitance capacitors are made of polyester (nF) and
ceramic (pF).
For large capacity values (µF) electrolytic capacitors are used. These
are polarised and marked with the maximum voltage.
Be careful not to connect electrolytic capacitors the wrong way or
across a higher voltage.
Polarised capacitor symbol
+
Ceramic and plastic capacitors
slide Slide 44
•What kind of capacitor is this?
It’s an e___________ c__________.
•Describe its characteristics?
Its value __________________
_____________________Volts.
It can work between _______________
Discuss with your partner what will happen if we use them in a 50V circuit?
I think it _____________
because ________________________
6c. After reading the text answer the questions.
slide Slide 45
•What kind of capacitor is this?
It’s an electrolytic capacitor.
•Describe its characteristics?
Its value is 4700 µF.
Its maximum voltage is 25 Volts.
It can work between -40º and 85 ºC.
Discuss with your partner what will happen if we use them in a 50V circuit?
6c. After reading the text answer the questions.
I think it will explode
because it can only stand 25 V.
slide Slide 46
Usually we connect a CAPACITOR IN SERIES WITH A RESISTOR FOR
TIMING purposes. The flow of current through a resistor into the capacitor
charges it until it reaches the same voltage than the power supply.
7a . Analyse the diagrams and try to sequence the text with your partner putting order numbers in the empty cells.
Vc R
S1
CS2 Vo
Vo
Time1 2 3 4 5 6 7 8 9 10
Vc
Charge Discharge
slide Slide 47
7a . Put order numbers in the empty cells to sequence the text.
Vc R
S1
CS2 Vo
Vo
Time1 2 3 4 5 6 7 8 9 10
Vc
Charge Discharge
A The capacitor starts discharging sharply through R.
B S1 is switched off and S2 is switched on.
C At the beginning switch 1 and 2 are off. 1
D The capacitor starts charging fast through R.
E The capacitor is fully discharged.
F S1 is switched on.
G Vo rises slowly as it approximates Vc.
H The capacitor is fully charged at Vc.
I The voltage across the capacitor rises sharply.
J Vo decreases slowly as it approaches 0V.
slide Slide 48
7a . Put order numbers in the empty cells to sequence the text.
Vc R
S1
CS2 Vo
Vo
Time1 2 3 4 5 6 7 8 9 10
Vc
Charge Discharge
A The capacitor starts discharging sharply through R. 8
B S1 is switched off and S2 is switched on. 7
C At the beginning switch 1 and 2 are off. 1
D The capacitor starts charging fast through R. 3
E The capacitor is fully discharged. 10
F S1 is switched on. 2
G Vo rises slowly as it approximates Vi. 5
H The capacitor is fully charged at Vc. 6
I The voltage across the capacitor rises sharply. 4
J Vo decreases slowly as it approaches 0V. 9
slide Slide 49
The time it takes to charge a capacitor depends on a time constant called tau. Tau depends on the resistor and the capacitor.
τ = R · C
The total charging time (tc) is approximately 4 times this time constant.
tc = 4 τ
slide Slide 50
•What % of the final voltage does the capacitor reach after τ? And after 4τ?
•Calculate the time constant for R=100 kΩ and C=100µF.
•What happens to the charging time if we halve the value of the resistor?
•What happens to the charging time if we double the value of the capacitor?
7b.
slide Slide 51
•What % of the final voltage does the capacitor reach after τ? And after 4τ?
After τ seconds the capacitor reaches 63.2% of Vc.
After 4τ seconds, the capacitor reaches 98.2% of the final voltage.
•Calculate the time constant for R=100 kΩ and C=100µF.
τ = R·C =100,000 · 0.0001 =10 seconds
•What happens to the charging time if we halve the value of the resistor?
We can predict that the time constant will be half of 10 seconds.
τ = R·C =50,000 · 0.0001 = 5 seconds
•What happens to the charging time if we double the value of the capacitor?
We can predict that the time constant will be the double of 10
seconds.
τ = R·C =100,000 · 0.0002 = 20 seconds
7b.
slide Slide 52
7c. Explain what actions the following graph describes. Pay special attention to what happens between 3 and 4, and between 5 and 6.
Vo
Time
1 2 3 4 5 6Vc
Vc R
S1
CS2 Vo
At the beginning, S1 and S2 are off. ...........................
At instant 2, switch 1 is ....................
slide Slide 53
Vo
Time
1 2 3 4 5 6
VcVc R
S1
CS2 V
o
At the beginning, S1 and S2 are off. The capacitor is not charged.
At instant 2, switch 1 is turned on. The capacitor starts charging fast through the resistor. Before instant 3 the capacitor is fully charged. At that moment S2 is switched on and the capacitor discharges instantly because there is no resistance.
Between 3 and 4 the resistance is adjusted to a higher value. At instant 2 S2 is switched off again and the capacitor starts charging slowly through the new R. It reaches Vc and stops charging until S2 is switched on again at instant 5. Then the capacitor discharges again.
Between 5 and 6 the resistance is adjusted to a lower value. At instant 6 S2 is switched off again and the capacitor charges faster this time because of the low resistance.
slide Slide 54
2.3. Diodes.
Semiconductors are materials that conduct electricity under certain
conditions. Silicon is the most used to make electronic components.
symbol
a k+ _
Vc
R
I+
Forward bias
Vc
R
I+
Reverse bias
A diode is a semiconductor device that allows current to flow in one
direction. It can be used for protection, to block signals, to change AC
to DC, etc.
The two leads are called anode (a or +) and cathode (k or -).
slide Slide 55
8a. Look at the diagrams above and fill in the blanks.
The current can only flow from ___________ to ___________.
This direction is called ____________ bias.
The current cannot flow from __________ to ____________.
This direction is called ____________ bias.
8b. The cathode is identified by a band on its body. Label the leads of these diodes as anode or cathode.
slide Slide 56
8a. Look at the diagrams above and fill in the blanks.
The current can only flow from anode to cathode.
This direction is called forward bias.
The current cannot flow from cathode to anode.
This direction is called reverse bias.
8b. The cathode is identified by a band on its body. Label the leads of these diodes as anode or cathode.
anode
cathode
cathode
anode
slide Slide 57
8c. Draw wires to connect this diode in direct biasing as seen in the circuit diagram. Explain how you have connected the wires to your partner.
Vc
R
I+
wire 2
wire 3
wire 1
The first wire goes from positive lead of the battery to....
slide Slide 58
8c. Draw wires to connect this diode in direct biasing as seen in the circuit diagram. Explain how you have connected the wires to your partner.
Vc
R
I+
wire 2
wire 3
wire 1
The first wire goes from positive lead of the battery to the anode of the diode.
The second wire goes from the cathode of the diode to a lead of the resistor.
The third wire goes from the other terminal of the resistor to the negative pole of the battery.
slide Slide 59
The voltage needed to operate the diode in forward bias is about 0.7 V.
Here you can see how to calculate the current in forward bias.
Vc
R
I+ 0.7 V
VR=Vc-0.7
Vc
R
I=0
+ Vc
0 V
slide Slide 60
9. Calculate the current (I) in these 3 circuits.
6 V
100 Ω
I+
a)
3 V
100 Ω
I+
b)
3 V
100 Ω
I+
c)
a)
b)
c)
slide Slide 61
9. Calculate the current (I) in these 3 circuits.
6 V
100 Ω
I+
a)
3 V
100 Ω
I+
b)
3 V
100 Ω
I+
c)
a)
b)
c)
slide Slide 62
Light-emitting diodes or LEDs are made from different semiconductor materials that give off light when connected in forward biasing.
The forward bias voltage can be between 1.6 V and 3.5 V depending on the
colour (2 V for red colour).
Usually an LED is connected in series with a resistor to limit the current between 20 mA and 30 mA. More current would fuse it
Vc R?
25 mA
+
2 V
VR=Vc-2
slide Slide 63
10. Is the LED in the circuit safe? Why (not)?
5 V 47Ω+
Red
Calculate the resistor value to set the current to 30 mA.
Calculate a new resistor value to set the current to 20 mA.
slide Slide 64
10. Is the LED in the circuit safe? Why (not)?
5 V 47Ω+
Red
- No, it isn’t.
- Because the current is 64 mA and it must be between 20 mA and 30 mA.
Calculate the resistor value to set the current to 30 mA.
Calculate a new resistor value to set the current to 20 mA.
slide Slide 65
11a. Look at the circuit and answer these questions. You can ask them to your partner.
5 V + 5 V
+
100 Ω
Red
a b
-Will the LED glow when the switch is at
position “a” ?
- ___ it w_____ because it is ________
biased.
-What will the voltage across the
resistor be?
- It will be _____________________
- Will the LED glow with the switch at position “b” ?
- ____ it _______ because it is _______ biased.
- What will the voltage across the resistor be?
- It will be ____________.
slide Slide 66
11a. Look at the circuit and answer these questions. You can ask them to your partner.
a
5 V + 5 V
+
100 Ω
Red
a b
-Will the LED glow when the switch is at
position “a” ?
- Yes it will because it is forward
biased.
-What will the voltage across the
resistor be?
- It will be 5-2 = 3 Volts
- Will the LED glow with the switch at position “b” ?
- No it won’t because it is reverse biased.
- What will the voltage across the resistor be?
- It will be 0 Volts.
slide Slide 67
11b. This circuit is a bridge rectifier. It is widely used to convert AC into DC.
Place 3 more diodes in the circuit so that the LED glows in both positions of the switch. Draw in blue the two diodes that conduct when the switch is at
position a. Draw in red the ones that conduct in position b.
5 V + 5 V
+
100 Ω
Reda b
What will the current through the through the resistor be?
slide Slide 68
11b. This circuit is a bridge rectifier. It is widely used to convert AC into DC.
Place 3 more diodes in the circuit so that the LED glows in both positions of the switch. Draw in blue the two diodes that conduct when the switch is at
position a. Draw in red the ones that conduct in position b.
5 V + 5 V
+
100 Ω
Reda b
What will the current through the through the resistor be?
slide Slide 69
2.4. Transistors.
12a. Listen to the text and fill in the blanks.
A transistor is a semiconductor device used to ________ and _________
electronic signals. We will focus on the common NPN bi-polar type of
transistors.
It has terminals for connection to an external circuit. The three leads are:
•The ______ (b), which is the lead responsible for activating the transistor.
•The collector (c), which is the _______ lead
•The emitter (e), which is the negative ________.
c
e
b NPN bi-polar transistor
Symbol Transistors in different packages
u2a12a.mp3
slide Slide 70
12a. Listen to the text and fill in the blanks.
When a small _______ flows through
the base-emitter circuit, a much larger
current flows through the collector-
emitter ________.
Ic= hFE · Ib
Ie=Ib+Ic
Ic=hFE·Ib
Ib
The gain (hFE) is the amount by which the transistor amplifies
current. Usual values are around 100.
slide Slide 71
12a. Listen to the text and fill in the blanks.
A transistor is a semiconductor device used to amplify and switch
electronic signals. We will focus on the common NPN bi-polar type of
transistors.
It has terminals for connection to an external circuit. The three leads are:
•The base (b), which is the lead responsible for activating the transistor.
•The collector (c), which is the positive lead
•The emitter (e), which is the negative lead.
c
e
b NPN bi-polar transistor
Symbol Transistors in different packages
slide Slide 72
12a. Listen to the text and fill in the blanks.
When a small current flows through
the base-emitter circuit, a much larger
current flows through the collector-
emitter circuit.
Ic= hFE · Ib
Ie=Ib+Ic
Ic=hFE·Ib
Ib
The gain (hFE) is the amount by which the transistor amplifies
current. Usual values are around 100.
slide Slide 73
12b. Calculate the Ib and Ie for the given Ib and hFE as in the example.
Ic=?
Ie=?
Ib=2 mAhFE=100
Ic = hFE · Ib = 100·2mA = 200 mA = 0.2 A
Ie = Ib+Ic = 2+200 = 202 mA = 0.202 A
a) Ib=0.1 mA; hFE=80 b) Ib=12 mA; hFE=120
c) Can you calculate the Ib that we need to get Ic=0,3A if hFE=150?
Ic=0,3 A
Ie
Ib=?hFE=150
slide Slide 74
12b. Calculate the Ib and Ie for the given Ib and hFE as in the example.
Ic=?
Ie=?
Ib=2 mAhFE=100
Ic = hFE · Ib = 100·2mA = 200 mA = 0.2 A
Ie = Ib+Ic = 2+200 = 202 ma = 0.202 A
a) Ib=0.1 mA; hFE=80 b) Ib=12 mA; hFE=120
c) Can you calculate the Ib that we need to get Ic=0,3A if hFE=150?
Ic=0,3 A
Ie
Ib=?hFE=150
Ic= hFE · Ib=80·0.1mA=8 mA= 0.008 A
Ie = Ib+Ic=0.1+8=8.1 mA=0.0081 A
Ic = hFE · Ib = 120·12mA=1440 mA = 1.44 A
Ie = Ib+Ic=12+1440 =1452 mA =1.452 A
slide Slide 75
As with diodes, a voltage of 0.7V is necessary
across the base-emitter to activate the transistor.
12c. Find out Ib and Ic for these values: Vbb=3V; Rb=100Ω; hFE=100
Ic=hFE·Ib
Ie
Vcc
Vbb Rb
In this circuit you can see the
formula to calculate the current
into the base. Then you can
calculate the current into the
collector.
slide Slide 76
As with diodes, a voltage of 0.7V is necessary
across the base-emitter to activate the transistor.
12c. Find out Ib and Ic for these values: Vbb=3V; Rb=100Ω; hFE=100
Ic=hFE·Ib
Ie
Vcc
Vbb Rb
In this circuit you can see the
formula to calculate the current
into the base. Then you can
calculate the current into the
collector.
slide Slide 77
13a. Discuss with your partner and find two ways to make the light bulb glow brighter in the last circuit.
If we increase/decrease Vbb
If collector current goes up/down
If base current goes up/down
then
base current will go up/down
the light bulb will glow brighter /dimmer
collector current goes much higher/lower.
a) One way to make the light bulb glow brighter is to increase ...........
because then ..................................................................................
………………………………………………………………..…………
b) Another way to do it
is .................................................................... ...................................
.....................................................................
slide Slide 78
13a. Discuss with your partner and find two ways to make the light bulb glow brighter in the last circuit.
If we increase/decrease Vbb
If collector current goes up/down
If base current goes up/down
then
base current will go up/down
the light bulb will glow brighter /dimmer
collector current goes much higher/lower.
a) One way to make the light bulb glow brighter is to increase Vbb
because then the base current will go up. As a result the collector
current will go much higher and the light bulb will glow brighter.
b) Another way to do it is to lower the resistance value of Rb.
slide Slide 79
In this circuit the transistor
works as a CURRENT
AMPLIFIER. Ic=hFE·IbVcc
Rb
P
Ib
1. The potentiometer...........................
2. Moving the cursor up is like.............
3. To make the light bulb glow
dimmer.
4. The collector current is controlled....
a) you have to move the cursor down.
b) by the potentiometer.
c) works as a potential divider.
d) making Vbb higher in exercise 12a.
13b. Match sentence beginnings with endings.
slide Slide 80
In this circuit the transistor
works as a CURRENT
AMPLIFIER. Ic=hFE·IbVcc
Rb
P
Ib
1. The potentiometer...........................
2. Moving the cursor up is like.............
3. To make the light bulb glow
dimmer.
4. The collector current is controlled....
c) works as a potential divider.
d) making Vbb higher in exercise 12a.
a) you have to move the cursor down.
b) by the potentiometer.
13b. Match sentence beginnings with endings.
slide Slide 81
In many cases we don’t need to control the collector current in a
continuous analogue way. We just want 2 states.
It works as a DIGITAL SWITCH controlled by the base current:
Ie
VccRb
Rc
Ib=0
S1
Ic=0
A1)
Ic>>0
Ie
VccRb
Rc
Ib>0
S1
A2)
ONOFF
•OFF: Ic=0 because Ib=0 or voltage across base-emitter is lower than 0.7 V.
•ON: Ib is the maximum possible in the circuit because Ic is high.
slide Slide 82
14a. Identify which circuit the two descriptions refer to, A or B.
Ie
VccRb
Rc
Ib=0OFF
S1 0 V
Ic=0
+-
B2)
Circuit ___ : When the switch is ON a current passes through the resistor into the base of the transistor. Then the transistor allows collector current to flow and the LED comes on.
Circuit ___ :When the switch is ON the voltage across base-emitter comes to 0. Then the transistor doesn’t allow collector current to flow and the LED goes off.
Ie
VccRb
Rc
Ib>0 ON
S1 0.7 V
Ic>>0
+
-
B1)
slide Slide 83
14a. Identify which circuit the two descriptions refer to, A or B.
Circuit A : When the switch is ON a current passes through the resistor into the base of the transistor. Then the transistor allows collector current to flow and the LED comes on.
Circuit B :When the switch is ON the voltage across base-emitter comes to 0. Then the transistor doesn’t allow collector current to flow and the LED goes off.
Ie
VccRb
Rc
Ib>0 ON
S1 0.7 V
Ic>>0
+
-
B1)
Ie
VccRb
Rc
Ib=0
S1
Ic=0
A1)
OFF
slide Slide 84
14b. In this circuit the transistor also works as a SWITCH. The capacitor charges through Rb. Rb and C form a voltage divider for timing purposes.
Try to predict how the circuit works.
VccRb
Rc
Ib
S1 Vbe
Ic
+
-+Icap
C
When S1 is
on ............................................ ........
..........................................................
...... ...................................................
..................... ................. and the
LED is ..............
When S1 is off the
capacitor ................ .........................
.................. and the LED
is .................. When voltage across
the capacitor reaches .....
V .......................... ............................
........................................... ..............
.. and the LED is ......
until ......... ........................................
.....
slide Slide 85
14b. In this circuit the transistor also works as a SWITCH. The capacitor charges through Rb. Rb and C form a voltage divider for timing purposes.
Try to predict how the circuit works.
VccRb
Rc
Ib
S1 Vbe
Ic
+
-+Icap
C
When S1 is on the voltage across
base-emitter comes to 0. Then the
transistor doesn’t allow collector
current to flow and the LED is off.
When S1 is off the capacitor starts
charging through Rb and the LED is
off. When voltage across the
capacitor reaches 0.7 V current
passes through the base, collector
current flows and the LED is on until
S1 is switched on again.
slide Slide 86
RECTIFIER BRIDGE.
Ra b
c
dVin +
slide Slide 87
LIGHT REGULATOR.
Ic=hFE·IbVcc
Rb
P
Ib
Rc
slide Slide 88
TIMER.
Vcc P
Rc
Ib
S1 Vbe
Ic
+-+Icap
C
slide Slide 89
SELF ASSESSMENT.
QUESTION NoMore or less Yes
Can I get the value of a resistor using the colour code and use multiples to express it?
Can I list the different types of resistors, draw their symbols and explain possible applications?
Can I calculate voltage in simple voltage dividers?
Can I describe and calculate charge and discharge of a capacitor in RC circuits?
Can I calculate currents in circuits with diodes and resistors?
Can I explain how a transistor works in a circuit, both as a switch or as an amplifier?
Can I interpret diagrams and identify components to build simple circuits?
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